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The Rotation - Activity relation

Stars across the Hertzsprung-Russell diagram are known to emit X-rays with only a few exceptions. For solar- and late-type stars the X-rays come from a magnetically confined plasma at temperatures of several million Kelvin known as a corona (Vaiana et al. 1981). The corona is believed to be powered by the stellar magnetic dynamo, which itself is thought to be driven by differential rotation in the stellar interior (e.g. Parker 1955). As stars age they spin down and therefore the dynamo weakens and so does the coronal X-ray emission from stars. The rotational spin-down is driven by mass-loss through a magnetized stellar wind, which is also driven by the stellar dynamo, effectively creating a feedback loop in which rotation and stellar activity decrease with age.

Understanding the relationship between rotation and activity is important for an understanding of stellar dynamos, magnetism and activity, relevant both to stars and our Sun. Solar activity influences Earth's magnetosphere and can also disrupt communication satellites and the power grid. Such activity can also influence extra-solar planets, including the properties of planetary atmospheres and the development of life. For all these reasons it is important to understand the stellar dynamo, and in particular to quantify the relationship between rotation and activity that characterizes the dynamo.

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Read about my recent detailed study of the relation between stellar rotation and tracers of magnetic activity in Wright et al. 2011b, or read about our deep study of stellar X-ray sources in the Chandra COSMOS field in Wright, Drake & Civano 2010.